Abstract: With the technique of stable isotope15 N-traced urea, a field experiment was conducted to determine the effects of urease inhibitor(UI) and nitrification inhibitor(NI) on losses of ammonia(NH3) volatilization from paddy fields. The urease inhibitor NBPT ［N-(n-butyl) thiophosphoric triamide］ and nitrification inhibitor DMPP ［3, 4-Dimethyl-1H-pyrazole phosphate］ were added to urea(U) with a rate of 10, 000 mg/kg urea. A randomized experimental design with five treatments and three replicates was used: 1) CK(no N fertilizer); 2) Urea only; 3) Urea + NBPT; 4) Urea + DMPP; 5) Urea + NBPT + DMPP. The fertilizer was broadcast in rice field before the transplanting of rice seedlings. The results show that the losses of NH3 volatilization from the nitrogen fertilizers last for 21 days and the maximum volatilization turns up in the 4th day after fertilization. Compared to the urea treatment, the peak of volatilization and cumulative loss of NH3 from addition of NBPT significantly decreased by 27.04% and 21.65%, and that from combined addition of NBPT and DMPP decreased by 12.95% and 13.58%, respectively. On the contrast, adding DMPP alone enhanced the peak of NH3 volatilization by 23.61%, the NH3 losse did not increase significantly. NH3 volatilization rate is significantly correlated with the concentration of NH+4-N and pH of floodwater(P0.01), not significantly correlated with the temperatures of air, soil and floodwater. Therefore, the NH+4-N concentration and pH of floodwater are the dominating factors influncing NH3 volatilization rate. Compared to the normal urea, the two treatments added with NBPT increase yield of rice significantly, and combination of NBPT and DMPP markedly improves the recovery of applied N in the above-ground parts. In summary, the effects of urea added with urease inhibitor or combination of urease and nitrification inhibitors are better than urea added with nitrification inhibitor alone, in view of reduction of NH3 volatilization, increase of rice yield and the recovery of applied N in the above-ground parts.